Conventional fluidized bed type reactors operate as a columnar chamber through which there is an upflow of a fluid that suspends or fluidizes particles into an expanded bed. The particulates tend to migrate throughout the bed, usually at a slow rate, but they are contained within the bed while the fluid progresses through the suspended particles as essentially a front or in "plug flow." The particulates are typically catalysts such as biocatalyst beads, or feed material such as coal. The fluid phase (gas, liquid, or a mixture of the two) is typically a feed material or reactant at the reactor inlet, and a product and/or waste material at the reactor outlet.
For some applications, it is desirable to have means for continuously removing a product constituent from the fluid phase. This would be particularly useful in fluidized bed bioreactors where the retained particulates are immobilized biocatalysts that may be inhibited by the build-up of the product concentration.
Fluidized bed reactors have been used in the chemical process industry for many years, and such reactors utilizing immobilized biocatalysts have been studied for continuous fermentation and other bioreactor applications. A high productivity ethanol fermentation in an immobilized-cell fluidized-bed bioreactor has been demonstrated as disclosed in B. H. Davison and C. D. Scott, Applied Biochemistry and Biotechnology, Vol. 18, p. 19 (1988). Other uses for fluidized bed bioreactors are disclosed in U.S. Pat. No. 4,846,964, issued on Jul. 11, 1989. Although reactor systems, particularly bioreactors, may already operate with three phases (gas, liquid, solid), it has been suggested by H. Y. Wang, Annals New York Academy Sciences, Vol. 413, p. 313 (1983), that the addition of a separations agent (sorbent or solvent) may also be useful so that the conversion and separation step can be carried out simultaneously. It has been disclosed by S. S. Lee and H. Y. Wang, Biotechnology and Bioengineering Symposium, No. 12, p. 221 (1982), that solid sorbents can be added to stirred-tank reactors. Solvents can be used to extract product in membrane reactors, as disclosed by G. T. Frank and K. K. Sirkar, Biotechnology and Bioengineering Symposium. No. 17, p. 303 (1986). Another process which utilizes liquid product extraction technology is taught by R. M. Busche, et al, Applied Biochemistry and Biotechnology, Vol. 20/21, p. 357 (1989). Since many possible organic solvents are also toxic or inhibitory to microorganisms or enzymes, the use of continuous solvent extraction in fluidized bed bioreactor systems does not appear to be generally useful.
Methods for preparing gel beads useful in carrying out the present invention are found in C. D. Scott, Annals of the New York Academy of Sciences, Vol. 501, p. 487 (1987). Further work discussing fundamental hydrodynamics is disclosed by B. H. Davison, Applied Biochemistry and Biotechnology, Vol. 20/21, p. 449 (1989). Still further work which discusses biocatalyst bead properties is found in C. D. Scott, et al., Enzyme Microb. Technol., Vol. 11, p. 258 (1989).